Low Pressure Drop Fin with Selective Micro Surface Enhancement

ABSTRACT

The assembly includes a heat exchanger assembly including a plurality of tubes extending between first and second manifolds. A plurality of fins extend back and forth between and long the tubes in a continuous patch and define a plurality of legs extending between the tubes. Each of the legs includes a plurality of front long louvers for conveying a stream of air through the legs. Each of the legs further defines a plurality of main spoilers between the front long louvers and the back edges of the legs for inducing turbulence in the stream of air with each of the main spoilers having a spoiler height in the range of 50 to 90 percent of the long louver height and each of the main spoilers having a spoiler length in the range of 10 to 35 percent of the long louver length.

BACKGROUND OF THE INVENTION

1. Field of the Invention

A heat exchanger assembly, and more specifically, a heat exchangerassembly including louvered air fins for transferring heat between arefrigerant and a stream of air.

2. Description of the Prior Art

A vast number of heat transfer applications, e.g. residential HVAC,electronics, etc., operate under very low thermal heat transferpotential. In other words, the temperature difference between therefrigerant and the stream of air entering the heat exchanger is notgreat. Additionally, the size and power of the fan propelling the streamof air through a heat exchanger is often limited by a number ofconstraints, e.g. power usage, noise, space, etc. For example, in alaptop computer, the size of the fan must be minimized to fit within thespace constraints of the casing, and the power of the fan must beminimized to avoid draining the battery or producing undesirable noise.In these applications, the performance of the air fins in transferringheat between the refrigerant and the stream of air is critical. Air finsgenerally include louvers to increase heat transfer, but those louversalso create an undesirable pressure drop in the stream of air.

U.S. Patent Application Publication No. 2008/0121385, to In Chuil Kim(hereinafter referred to as Kim '385) shows a heat exchanger assemblyfor transferring heat between a refrigerant and a stream of air. Kim'385 includes first and second manifolds spaced from one another. Aplurality of tubes extend in spaced relationship with one anotherbetween the first and second manifolds for conveying the refrigerantbetween the first and second manifolds. A plurality of fins are disposedbetween adjacent tubes for transferring heat between the tubes and thestream of air. Each of the fins has a front edge and a back edge andpresents a plurality of legs extending transversely between the adjacenttubes. Each of the legs of the fins defines a plurality of front longlouvers disposed between the front and back edges for conveying thestream of air through the legs of the air fins with each of the longlouvers having a long louver height and a long louver length.

SUMMARY OF THE INVENTION AND ADVANTAGES

The invention provides for such a heat exchanger assembly and whereineach of the legs of the fins defines a plurality of main spoilersdisposed between the front long louvers and the back edges for inducingturbulence in the stream of air with each of the main spoilers having aspoiler height in the range of 50 to 90 percent of the long louverheight and each of the main spoilers having a spoiler length in therange of 10 to 35 percent of the long louver length.

The potential for heat transfer between the refrigerant and the streamof air decreases as the air flows downstream through the heat exchangerbecause the temperature difference between the refrigerant and thestream of air is reduced. The long louvers have more potential for heattransfer than the main spoilers because the long louvers turn and induceturbulence to the stream of air, whereas the main spoilers functionmainly to induce turbulence in the air. Therefore, the long louvers aredisposed upstream, where the temperature difference between the streamof air and the refrigerant is greatest, of the main spoilers. Theupstream long louvers perform the majority of the heat transfer betweenthe stream of air and the refrigerant. Although long louvers are veryeffective at transferring heat between the stream of air and therefrigerant, they come at a cost. Namely, long louvers create a largepressure drop in the stream of air flowing through the heat exchanger.Therefore, it is undesirable to have long louvers extend the entirelength of the air fin. The smaller main spoilers are disposed downstreamof the long louvers to induce turbulence in the stream of air toincrease the air's heat transfer potential without compromising theoverall pressure drop of the heat exchanger. This allows for a greaterquantity of air to flow through the upstream long louvers of the finsand improves the overall efficiency of the heat exchanger assembly.

BRIEF DESCRIPTION OF THE DRAWINGS

Other advantages of the present invention will be readily appreciated,as the same becomes better understood by reference to the followingdetailed description when considered in connection with the accompanyingdrawings wherein:

FIG. 1 is a perspective view of a heat exchanger assembly;

FIG. 2 is a perspective view, partially cut away a first embodiment of afin with louvers and one tube of a heat exchanger assembly;

FIG. 3 is a front view, partially cut away of a first embodiment of afin;

FIGS. 4 a through f are cross-sectional views of the first through sixthembodiments of the louvers and spoilers of the fins;

FIG. 5 is a cross-sectional view showing the flow of air over thelouvers and spoilers according to one of the embodiment of FIG. 4 a; and

FIG. 6 is a front view, partially cut away for an alternate embodimentof a fin having micro-louvers disposed in a staggered arrangement.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

Referring to the Figures, wherein like numerals indicate correspondingparts throughout the several views, a heat exchanger assembly 20 fortransferring heat between a refrigerant and a stream of air 22 isgenerally shown in FIG. 1.

Referring to FIG. 1, the heat exchanger assembly 20 includes a firstmanifold 24 and a second manifold 26 extending in spaced and parallelrelationship with one another. The first manifold 24 defines a pluralityof first tube slots 28 being spaced from one another. The secondmanifold 26 defines a plurality of second tube slots 30 being spacedfrom each other and aligned with the first tube slots 28. A plurality oftubes 32 extend in spaced and parallel relationship to one anotherbetween the aligned first and second tube slots 28, 30. Each of thetubes 32 has a cross-section defining flat sides 34 interconnected by around front 36 and a round back 38. Each of the tubes 32 defines a fluidpassage 40 for conveying refrigerant between the manifolds 24, 26.

A plurality of fins 42, generally indicated, are disposed betweenadjacent ones of the tubes 32 for transferring heat between therefrigerant in the fluid passages 40 of the tubes 32 and the stream ofair 22. The fins 42 have a fin height H_(F). The fins 42 extendcontinuously between a front edge 44 adjacent to the round front 36 ofthe tubes 32 and back edge 46 adjacent to the round back 38 of the tubes32. In other words, the front edge 44 of the fins 42 is upstream of theback edge 46 of the fins 42. Each of the fins 42 includes a plurality oflegs 48 extending transversely between the adjacent tubes 32. The fins42 also include a plurality of end portions 50 engaging the flat sides34 of the adjacent tubes 32. Together, the legs 48 and end portions 50of the fins 42 present a serpentine path extending between the first andsecond manifolds 24, 26. In other words, adjacent legs 48 of the fins 42are connected by end portions 50 engaging opposite ones of the flatsides 34 of the adjacent tubes 32.

In all of the embodiments of the subject invention, shown in FIGS. 4a-f, each of the legs 48 of the fins 42 presents a plurality of frontlong louvers 52 disposed between the front and back edges 44, 46. Inaddition to inducing turbulence in the stream of air 22, the front longlouvers 52 function to turn the stream of air 22. In other words, thefront long louvers 52 convey the stream of air 22 through the legs 48 ofthe air fins 42. This keeps the stream of air 22 in the heat exchangerlonger and gives the stream of air 22 more time to receive heat from ordispense heat to the refrigerant in the tubes 32, depending on theapplication of the heat exchanger assembly 20. The long louvers 52, 54have a long louver height H_(L), which is preferably in the range of 60to 90 percent of the fin height H_(F), and the long louvers 52, 54 havea long louver length L_(L), which is preferably in the range of 0.7 to1.5 mm.

In all of the embodiments of the subject invention, shown in FIGS. 4a-f, each of the legs 48 of the fins 42 presents a plurality of mainspoilers 56, 58, 60 disposed between the front long louvers 52 and theback edge 46, i.e. downstream of the front long louvers 52. The mainspoilers 56, 58, 60 serve to interrupt the airflow and induce turbulencein the stream of air 22, but do not substantially turn the air as thefront long louvers 52 do. In other words, although some air might beconveyed cross-stream between the legs 48 of the fins 42 through themain spoilers 56, 58, 60, the majority of the air is flows straightthrough the heat exchanger assembly 20. Each of the main spoilers 56,58, 60 has a spoiler height H_(s) preferably in the range of 50 to 90percent of the long louver height H_(L), and each of the main spoilers56, 58, 60 has a spoiler length L_(S) preferably in the range of 10 to35 percent of the long louver length L_(L). A small spoiler length L_(S)compared to the long louver length L_(L) keeps the airflow blockage dueto the main spoilers 56, 58, 60 small, thereby achieving good heattransfer with a low pressure drop penalty.

As shown in FIGS. 4 a-f, each of the legs 48 of the fins 42 issymmetrical. In other words, all of the embodiments include back longlouvers 54 disposed between the main spoilers 56, 58, 60 and the backedge 46 of the air fin 42. Additionally, some of the embodiments includeback spoilers 62 disposed between the back long louvers 54 and the backedge 46 of the air fin 42. The symmetry of the fins 42 is primarily formanufacturing purposes because symmetrical fins 42 can be made lessexpensively than non-symmetrical fins 42. It should be appreciated thatthe main spoilers 56, 58, 60 could extend from the front long louvers 52to the back edge 46, or the air fin 42 could be flat between the mainspoilers 56, 58, 60 and the back edge 46.

In the first embodiment, shown in FIG. 4 a, each of the legs 48 of thefins 42 presents a plurality of front spoilers 64 adjacent to the frontedge 44 for interrupting the flow and inducing turbulence in the streamof air 22. The delta-wing, or triangular, shaped front spoilers 64 arebest shown in FIGS. 2 and 3. The delta wings are disposed over theentire fin height H_(F). The width and height of the delta-wings iscomparable to the spoiler length L_(S). The front spoilers 64 are mostuseful when used in a cold environment. In cold environments, frost hasa tendency of building up on the front edge 44 of the fins 42 when thereis large heat transfer rate between the air and the refrigerant at thatfront edge 44. The frost can block the stream of air 22 from flowingthrough the heat exchanger, which drastically reduces the efficiency ofthe heat exchanger. The front spoilers 64 disposed upstream of the frontlong louvers 52 ensure that the maximum rate of heat transfer takesplace slightly downstream of the front edge 44 of the fins 42 to preventthe frost from building up on the front edge 44 of the fins 42. Althoughthe efficiency of the heat exchanger assembly 20 might be reduced insome operating conditions, i.e. in warm environments, heat exchangerassemblies 20 having front spoilers 64 can be used in a wider variety ofoperating conditions. The main spoilers 56, 58, 60 of the firstembodiment are micro-louvers 56.

The second embodiment, shown in FIG. 4 b, is similar to the firstembodiment, but the delta-wing shaped front spoilers 64 of the firstembodiment are replaced with front micro-louvers 64, shaped similarly tothe main spoilers 56, 58, 60. The front micro-louvers 64 functionsimilar to the delta-wing shaped front spoilers 64 of the firstembodiment in that they interrupt the airflow and induce turbulence inthe air, but leave the majority of the heat transfer to the long louvers52, 54 disposed between the micro-louvers 64 and the main spoilers 56,58, 60, which are also shown as micro-louvers 56.

The third embodiment, shown in FIG. 4 c, has front long louvers 52disposed upstream of the main spoilers 56, 58, 60, shown asmicro-louvers 56. Because the third embodiment does not have frontspoilers 64, airflow is steered in the cross stream direction by thefront and back long louvers 52, 54. Airflow is mostly straight in themid section.

Like the third embodiment, the fourth embodiment, shown in FIG. 4 d,shows the main spoilers 56, 58, 60 as being micro-louvers 56. Themicro-louvers 56 of the fourth embodiment extend outwardly on both sidesof the legs 48 of the fins 42.

The fifth embodiment, shown in FIG. 4 e, shows the main spoilers 56, 58,60 as being semi-cylindrical bumps 58. The semi-cylindrical bumps 58extend outwardly on both sides of the legs 48 of the fins 42.

The sixth embodiment, shown in FIG. 4 f, shows the main spoilers 56, 58,60 as being triangular notches 60. The triangular notches 60 extendoutwardly from the leg 48 on opposite sides of the leg 48.

It should be appreciated that the main spoilers 56, 58, 60 may take anynumber of shapes, not just those shown in FIGS. 4 a-f. The main spoilers56, 58, 60 can be disposed both upstream or downstream of at least onefront long louver 52. Additionally, each of the main spoilers 56, 58, 60must have a spoiler height H_(S) in the range of 50 to 90 percent of thelong louver height H_(L), and each of the main spoilers 56, 58, 60 musthave a spoiler length L_(S) in the range of 10 to 35 percent of the longlouver length L_(L).

In applications where the maximum thermal potential for total heatdissipation is small, it is paramount that total airflow through theheat exchanger assembly 20 be high. With fan power and noiseconstraints, airflow can be high only when the overall pressure drop ofthe heat exchanger is kept to a minimum. Having front spoilers 64, asshown in FIGS. 4 a-c, allows the flow a better entrance condition intothe core of the heat exchanger with a low pressure drop but with someheat transfer enhancement as compared to an un-louvered surface. In thisfashion high pressure drop is expended locally only where heat transferpotential is maximum without compromising the tendency of frost to buildup on the front edges 44 of the fins 42. The bulk of the heat transferbetween the refrigerant and the stream of air 22 occurs at the frontlong louvers 52. The rest of the fin 42 is utilized for pressure dropmanagement with some heat transfer augmentation through the mainspoilers 56, 58, 60 downstream of the front long louvers 52.

FIG. 5 shows the stream of air 22 flowing through the heat exchangerassembly 20 of the first embodiment. As shown, the air flows straightbetween the legs 48 of the fins 42 past the micro-louvers or thedelta-wing shaped front spoilers 64. As the stream of air 22 flowsdownstream between the legs 42, most of the air is turned by the frontlong louvers 52 between the legs 42. The stream of air 22 thenstraightens out as it passes the main spoilers 56, 58, 60. The back longlouvers 54, which are optional as explained above, turn the stream ofair 22 again between the legs 42. The stream of air 22 once againstraightens out when it passes the delta-wing shaped back spoilers 62.Although not shown in FIG. 5, it should be appreciated that each of thefront spoilers 64, front long louvers 52, main spoilers 56, 58, 60, backlong louvers 54, and back spoilers 62 induces turbulence into the streamof air 22. The micro-louver segment can be disposed anywheresymmetrically or asymmetrically within the fins 42.

As shown in FIG. 6, the micro-louvers 56 can alternately be disposed ina staggered arrangement. The staggered arrangement can be easilymanufactured and provide for a large number of micro-louvers 56 with asmaller pressure drop penalty. Additionally, the staggered micro-louvers56 are disposed close to the end portions 50 of the fins 42, which havethe a higher heat transfer potential than the middle of the fins 42.

While the invention has been described with reference to an exemplaryembodiment, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted forelements thereof without departing from the scope of the invention. Inaddition, many modifications may be made to adapt a particular situationor material to the teachings of the invention without departing from theessential scope thereof. Therefore, it is intended that the inventionnot be limited to the particular embodiment disclosed as the best modecontemplated for carrying out this invention, but that the inventionwill include all embodiments falling within the scope of the appendedclaims.

1. A heat exchanger assembly for transferring heat between a refrigerantand a stream of air, comprising: a first manifold; a second manifoldspaced from said first manifold; a plurality of tubes extending inspaced relationship with one another between said first and secondmanifolds for conveying the refrigerant between said first and secondmanifolds; a plurality of fins disposed between adjacent ones of saidtubes for transferring heat between the refrigerant in said tubes andthe stream of air; each of said fins having a front edge and a back edgeand including a plurality of legs extending transversely between saidadjacent tubes; each of said legs of said fins defining a plurality offront long louvers disposed between said front and back edges forconveying the stream of air through said legs of said air fins with eachof said long louvers having a long louver height and a long louverlength; and each of said legs of said fins defining a plurality of mainspoilers disposed between said front long louvers and said back edgesfor inducing turbulence in the stream of air with each of said mainspoilers having a spoiler height in the range of 50 to 90 percent ofsaid long louver height and each of said main spoilers having a spoilerlength in the range of 10 to 35 percent of said long louver length. 2.The assembly as set forth in claim 1 wherein said main spoilers aremicro-louvers.
 3. The assembly as set forth in claim 1 wherein each ofsaid legs of said air fins presents a plurality of front spoilersdisposed between said front edge and said front long louvers forinducing turbulence in the stream of air.
 4. The assembly as set forthin claim 3 wherein each of said front spoilers extends outwardly fromsaid legs and has a triangular shape.
 5. The assembly as set forth inclaim 3 wherein each of said legs of said air fins defines a pluralityof back spoilers disposed adjacent to said back edge and a plurality ofback long louvers disposed between said micro-louvers and said backspoilers.
 6. The assembly as set forth in claim 1 wherein each of saidlegs of said fins has a fin height and said long louver height is in therange of 50 to 90 percent of said fin height.
 7. The assembly as setforth in claim 1 wherein said long louver length is in the range of 0.7to 1.5 mm.
 8. The assembly as set forth in claim 1 wherein said spoilerlength is in the range of 0.15 to 0.4 mm.
 9. The assembly as set forthin claim 1 wherein each of said front long louvers extends diagonallyoutwardly from said legs of said fins.
 10. The assembly as set forth inclaim 1 wherein said first and second manifolds extend in spaced andparallel relationship with one another.
 11. The assembly as set forth inclaim 10 wherein said first manifold defines a plurality of first tubeslots spaced from one another and said second manifold defines aplurality of second tube slots spaced from one another and aligned withsaid first tube slots.
 12. The assembly as set forth in claim 11 whereineach of said tubes has a cross-section presenting flat sidesinterconnected by a round front and a round back.
 13. The assembly asset forth in claim 12 wherein said tubes extend in spaced and parallelrelationship with one another between said aligned first and second tubeslots of said first and second manifolds.
 14. The assembly as set forthin claim 1 wherein each of said tubes defines a fluid passage forconveying the refrigerant between said manifolds.
 15. The assembly asset forth in claim 1 where said main spoilers are disposed in astaggered arrangement.
 16. The assembly as set forth in claim 1 whereinsaid main spoilers are semi-cylindrical bumps.
 17. The assembly as setforth in claim 1 wherein said main spoilers are triangular notches. 18.A heat exchanger assembly for transferring heat between a refrigerantand a stream of air, comprising: a first manifold and a second manifoldextending in spaced and parallel relationship with one another; saidfirst manifold defining a plurality of first tube slots being spacedfrom each other; said second manifold defining a plurality of secondtube slots being spaced from each other and aligned with said first tubeslots; a plurality of tubes having a cross-section presenting flat sidesinterconnected by a round front and a round back and extending in spacedand parallel relationship with one another between said aligned firstand second tube slots for establishing fluid communication between saidfirst and second manifolds; each of said tubes defining a fluid passagefor conveying the refrigerant between said manifolds; a plurality offins disposed between adjacent ones of said tubes for transferring heatbetween the refrigerant in said fluid passages of said tubes and thestream of air; each of said fins including a plurality of legs with eachleg having a fin height and each leg extending transversely between saidadjacent tubes and each of said fins including a plurality of endportions extending along said flat sides of said adjacent tubes topresent a serpentine path between said first and second manifolds; eachof said legs of said fins having a front edge adjacent said round frontof said tubes and a back edge adjacent said round back of said tubes;each of said legs of said fins presenting a plurality of front spoilersadjacent to said front edge and a plurality of back spoilers adjacent tosaid back edge for inducing turbulence in the stream of air; each ofsaid front and back spoilers extending outwardly from said legs andhaving a conical shape; each of said legs of said fins presenting aplurality of front long louvers spaced from said front spoilers and aplurality of back long louvers spaced from said back spoilers forconveying the stream of air through said legs of said fins; each of saidlegs of said fins presenting a plurality of main spoilers disposedbetween said front long louvers and said back long louvers for inducingturbulence in the stream of air; each of said long louvers having a longlouver height in the range of 60 to 90 percent of said fin height; eachof said main spoilers having a spoiler height in the range of 50 to 90percent of said long louver height; each of said long louvers having along louver length in the range of 0.7 to 1.5 mm; and each of said mainspoilers having a spoiler length in the range of 10 to 35 percent ofsaid long louver length.